Conventionally, there has been known a monitoring control system provided with a controller which controls equipment such as a plant, and a monitoring control device which monitors and controls the controller through a network. In such monitoring control system, each device on the network is sometimes configured to cyclically perform cyclic transmission. The cyclic transmission is a data transmitting system for making contents of common memories provided on the devices on the network the same. In the cyclic transmission, each device on the network is configured to cyclically update the content of its own common memory by cyclically transmitting/receiving common data stored in its own common memory to/from other devices.
In the conventional monitoring control system described above, when desired control data is not stored in the common memory, the desired control data is generally acquired by one-to-one data communication performed separately from data communication by the cyclic transmission. Therefore, a processing load when acquiring the control data which is not stored in the common memory often becomes large.